Notch treatment methods for flaw simulation

ABSTRACT

A notch treatment method for flaw simulation including providing the specimen with the notch, the notch having a re-melt material layer; isolating the notch; and selectively etching the notch to provide an etched surface of the notch; wherein at least a portion of the re-melt material layer has been removed from the notch. In one aspect, there is provided a notch treatment method for flaw simulation including providing the specimen with the notch, the notch having a re-melt material layer, the specimen includes steel or an alloy thereof; isolating the notch; and selectively etching the notch with a first etching solution and a second etching solution to provide an etched surface on the notch; wherein at least a portion of the re-melt material layer has been removed from the notch.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.16/124,762, filed Sep. 7, 2018, which is a continuation-in-part of U.S.patent application Ser. No. 15/079,946, filed Mar. 24, 2016, whichclaims priority to U.S. provisional application No. 62/137,427, filedMar. 24, 2015, the disclosures of which are hereby incorporated byreference for all purposes as if fully set forth herein.

BACKGROUND Technical Field

The embodiments of the present disclosure relate to treatment methodsfor a notch on a specimen, such as a specimen used to determine damagetolerance allowables for an aircraft structure.

Description of Related Art

The United States Federal Aviation Federation (FAA) establishedairworthiness standards for aircraft such as airplanes and rotorcraftand provides airworthiness approval for aircraft, aircraft engines,propellers and related articles which certifies that they conform to anapproved design and are in a condition for safe operation. Morespecifically, part 29 of 14 CFR regulations is directed to airworthinessstandards for transport rotorcraft, which includes section § 29.571 thatis directed to fatigue tolerance evaluation of metallic structure. Thissection details fatigue tolerance substantiation of a principalstructure element (PSE) of a transport category rotorcraft. In addition,this section requires testing and evaluation of manufacturing flaws andoperational defects (“defects”). Crack initiation from the defect as afailure criterion is one of the seven methods to show compliance.

Conventional methods of determining damage tolerance allowables for anaircraft structure can include developing and testing specimens withvarious types and configurations of defects so as to cover all probablemanufacturing flaws and operational defects. With these methods, eithermultiple specimens having various types and configurations of defectsare used which can be laborious to prepare and test and requiresextensive analysis using a complicated testing matrix; or various typesand configurations of defects are simply represented by a crack, ofwhich fatigue tolerance analysis can result in the designing of aircraftstructures with too much conservatism, thus being heavier than actuallynecessary.

There is a need for an improved method of treating a defect (e.g., anotch) on a specimen. In particular, there is a need for an improvedmethod of treating a notch on a specimen, adequately representing adefect, used for fatigue tolerance substantiation.

SUMMARY

In a first aspect, there is a notch treatment method for flawsimulation, including providing a specimen with a notch, the notchhaving a re-melt material layer; isolating the notch; and selectivelyetching the notch to provide an etched surface of the notch; wherein atleast a portion of the re-melt material layer has been removed from thenotch.

In an embodiment, the step of providing the specimen with the notchincludes generating the notch on the specimen by electrical dischargemachining.

In an embodiment, the re-melt material layer is disposed on at least oneof a root notch and a lateral side wall of the notch.

In some embodiments, the specimen has a square cross-sectional portionand the notch is located in a corner of the square cross-sectionalportion.

In another embodiment, the specimen is at least one of the following:aluminum, titanium, magnesium, steel, or an alloy thereof.

In an embodiment, the step of isolating the notch includes placing anisolation layer with a slot onto the specimen such that the slot exposesthe notch.

In an exemplary embodiment, the step of isolating the notch furtherincludes placing a dam on the isolation layer to form a notch area and aperipheral area on the specimen; wherein the notch area is disposed atleast partially around the notch.

In a particular embodiment, the step of placing a dam on the isolationlayer includes forming a moldable cylinder.

In an embodiment, the step of selectively etching the notch includesapplying an etching solution to the notch area to form the etchedsurface on the notch.

In an illustrative embodiment, the etching solution includes at leastone of the following: a sodium hydroxide solution, a Kroll's etchantsolution, an acetic acid solution, an aqua regia solution, a Fry'sreagent solution, and a nital solution.

In an embodiment, the specimen includes aluminum or an alloy thereof;and the etching solution includes a sodium hydroxide solution.

In still yet another embodiment, the specimen includes titanium or analloy thereof; and the etching solution includes a Kroll's etchantsolution.

In an embodiment, the specimen includes magnesium or an alloy thereof;and the etching solution includes an acetic acid solution.

In another embodiment, the method further includes removing theisolation layer and the dam from the specimen; and cleaning the specimento remove the etching solution.

In an embodiment, at least a portion of the etched surface on the notchincludes microcracks.

In a second aspect, there is a notch treatment method for flawsimulation, including providing a specimen with a notch, the notchhaving a re-melt material layer, the specimen includes steel or an alloythereof; isolating the notch; and selectively etching the notch with afirst etching solution and a second etching solution to provide anetched surface on the notch; wherein at least a portion of the re-meltmaterial layer has been removed from the notch.

In an embodiment, the step of isolating the notch includes placing anisolation layer with a slot onto the specimen such that the slot exposesthe notch; and placing a dam on the isolation layer to form a notch areaand a peripheral area on the specimen; wherein the notch area isdisposed at least partially around the notch.

In a particular embodiment, the steel is a stainless steel alloy; thefirst etching solution includes an aqua regia solution; and the secondetching solution includes a Fry's reagent solution.

In an illustrative embodiment, the steel is a high strength steel alloy;the first etching solution includes an aqua regia solution; and thesecond etching solution includes a nital solution.

In an embodiment, the method further includes removing the isolationlayer and the dam from the specimen; cleaning the specimen to remove thefirst etching solution and the second etching solution; and applying aheat treatment to the specimen.

In an embodiment, at least a portion of the etched surface on the notchincludes microcracks.

Other aspects, features, and advantages will become apparent from thefollowing detailed description when taken in conjunction with theaccompanying drawings, which are a part of this disclosure and whichillustrate, by way of example, principles of the inventions disclosed.

DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the system and method ofthe present disclosure are set forth in the appended claims. However,the system and method itself, as well as a preferred mode of use, andfurther objectives and advantages thereof, will best be understood byreference to the following detailed description when read in conjunctionwith the accompanying drawings, wherein:

FIG. 1 is a side view of a rotorcraft, according to one exampleembodiment;

FIG. 2 is a schematic view of a method of determining damage toleranceallowables, according to one example embodiment;

FIG. 3 is a table, according to one example embodiment;

FIG. 4 is a schematic view of a method of manufacturing a part,according to one example embodiment;

FIG. 5 is a side view of a specimen, according to one exampleembodiment;

FIG. 6 is a cross-section view take at section lines 6-6 in FIG. 5,according to one example embodiment;

FIG. 7 is a detail view taken from FIG. 6, according to one exampleembodiment;

FIG. 8 is a stylized perspective view of a specimen, according to oneexample embodiment;

FIG. 9 is an illustrative specimen ID for a specimen, according to oneexample embodiment;

FIG. 10 is an illustrative da/dN vs. AK curve, according to one exampleembodiment;

FIG. 11 is a schematic view of a process of testing a specimen,according to one example embodiment;

FIG. 12 is a perspective view of a test setup that uses a potential drop(PD) to determine an occurrence of crack growth, according to oneexample embodiment;

FIG. 13 is a graph, according to one example embodiment;

FIG. 14 is a graph, according to one example embodiment;

FIG. 15 is a graph, according to one example embodiment;

FIG. 16 is a graph, according to one example embodiment;

FIG. 17 is a graph, according to one example embodiment;

FIG. 18 is a schematic view of a computer system, according to oneexample embodiment;

FIG. 19 a view of an EMD corner notch, according to one exampleembodiment;

FIG. 20 a close up view of an EMD corner notch before chemicalmodification, according to one example embodiment;

FIG. 21 a close up view of an EMD corner notch after chemicalmodification, according to one example embodiment;

FIG. 22 a close up cross-sectional view of a notch front and crack frontafter chemical modification, according to one example embodiment;

FIG. 23 is a graphical representation of a testing method, according toone example embodiment;

FIG. 24 is a graphical representation of threshold stress data,according to one example embodiment;

FIG. 25A is a close up view of an EMD corner notch before etching;

FIG. 25B is a close up view of the corner notch in FIG. 25A afteretching, according to one example embodiment;

FIG. 26A is a schematic view of a treatment method for a notch on aspecimen, according to one example embodiment;

FIG. 26B is a schematic view of a treatment method for a notch on aspecimen, according to an illustrative embodiment;

FIG. 27 is a top view of isolation layer with a slot, according to oneexample embodiment;

FIG. 28 is a side view of an isolation layer with a slot placed on aspecimen with a notch such that slot exposes the notch, according to anexemplary embodiment;

FIG. 29 is a top view of a dam disposed on the isolation layer on thespecimen, according to an exemplary embodiment;

FIG. 30 is a side view of the dam on the specimen in FIG. 29; and

FIG. 31 is a close up view of microcracks in an etched surface of thenotch root viewed from a cross-section of the center plane of the notch,according to one example embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Illustrative embodiments of the system and method of the presentdisclosure are described below. In the interest of clarity, all featuresof an actual implementation may not be described in this specification.It will of course be appreciated that in the development of any suchactual embodiment, numerous implementation-specific decisions must bemade to achieve the developer's specific goals, such as compliance withsystem-related and business-related constraints, which will vary fromone implementation to another. Moreover, it will be appreciated thatsuch a development effort might be complex and time-consuming but wouldnevertheless be a routine undertaking for those of ordinary skill in theart having the benefit of this disclosure.

In the specification, reference may be made to the spatial relationshipsbetween various components and to the spatial orientation of variousaspects of components as the devices are depicted in the attacheddrawings. However, as will be recognized by those skilled in the artafter a complete reading of the present disclosure, the devices,members, apparatuses, etc. described herein may be positioned in anydesired orientation. Thus, the use of terms such as “above,” “below,”“upper,” “lower,” or other like terms to describe a spatial relationshipbetween various components or to describe the spatial orientation ofaspects of such components should be understood to describe a relativerelationship between the components or a spatial orientation of aspectsof such components, respectively, as the device described herein may beoriented in any desired direction.

Damage tolerance allowables are essential for the damage tolerancedesign of rotorcraft structures, such as dynamic parts. When an aircraftis designed to certain usage and load conditions, the combination ofthose conditions flow down to the structures and translate into acertain stress level that depends upon the material composition of theparts and the detail design of the parts. A comparison of that stresslevel of the part to the damage tolerance allowables determines whetherthe part can satisfy the damage tolerance requirements with theparticular design. If the stress level exceeds the damage toleranceallowables, the part requires re-design to reduce the stress level ofthe part, which typically causes an increase in the weight of the partor a decrease in the overall load and usage capability of the aircraft.

If the damage tolerance allowables are overly conservative, the stresslevel of the part would have to be designed to meet the overlyconservative damage tolerance criteria, which would cause the size (andweight) of the part to increase to meet the given usage and loadrequirements of the aircraft. Alternatively, the usage and loadcapabilities of the aircraft would need to be lowered to maintain anyweight requirements.

Conventional ideology of determining damage tolerance requirementsincludes introduction of a crack in a critical location of a structureand analyzing the growth of that crack due to the aircraft usage andloading. Conventionally, in order to satisfy damage tolerancerequirements for high stress high frequency loaded rotorcraftstructures, the initial crack must not be allowed to grow. The term thatdescribes this “no growth” phenomena is called “threshold value.” Sincethe threshold values for small cracks were difficult to determine in thelaboratory, the conventional method (ASTM E647) determines thresholdvalues obtained by testing the long crack growth under decreasingloading until the crack stops growing. Based on threshold valuesobtained in such approximate ways, the small crack no-growth damagetolerance allowables are derived with further approximations andknockdowns. Multiple steps of approximations and derivations result inconservatism and variability, thus generating overly conservative damagetolerance allowables.

The present disclosure includes methods and systems of generatingno-growth damage tolerance allowables for structures, which allow forhigher stress level in the damage tolerant designed part with lessweight while meeting the usage and load requirements of the aircraft.Certain embodiments include methods and systems of directly obtainingno-growth damage tolerance allowables for aircraft structure, theallowables being approximately 15%-30% higher than allowables producedby the conventional ASTM E647 method. Moreover, a 15%-30% higherallowable can equate to an approximately 15%-30% weight savings of theaircraft structure. Furthermore, certain embodiments of the methods andsystems of directly obtaining no-growth damage tolerance allowables foraircraft structure may prevent the necessity of full scale aircraftstructure testing that may otherwise be required for certification. Themethod of the present application is a coupon specimen testing methodthat generates threshold stress data for fatigue crack initiation in ametallic material. In one embodiment, “threshold” can be the fatiguestress state {mean stress, oscillatory stress}, below which a flaw or acrack in a metallic material will not grow. As such, threshold stressmay also be called “no-growth threshold.”

In one embodiment, the test method generates threshold stress data forcrack initiation. The test specimen can be a square-bar coupon,cyclically loaded along the axis. Each coupon specimen contains a notchat a corner of the center-plane of the specimen to simulate a flaw.

Referring to FIG. 23, a graphic 2301 illustrates how the method derivesthe threshold stress. The test starts at required stress ratio R with aninitial load max 2305 and initial load min 2307. If crack initiationoccurs and the criterion Δa_(o)/ΔN≤4×10⁻⁹ in/cycle is met, this load isthe threshold fatigue load, from which the threshold stress of thematerial can be obtained. Otherwise if with that load the number ofcycle reaches No=1,000,000 without crack initiation, the load will bebumped up to a higher level and the test will be repeated. The number of1,000,000 cycles can be chosen because it meets the threshold criterionwith the maximum presumed crack initiation (0.004-in) even if it doesnot happen. This way the necessary conservatism of the data is ensured.This process can be repeated until crack initiation occurs at anoccurrence 2303 and the threshold criterion is not met. In this case,the previous load level will be used for no-growth threshold stress ofthe flaw.

Once the crack initiation occurs at the occurrence 2303, the testingcontinues and turns into determination of threshold stress for a crack,which becomes evident by a crack growth occurrence 2309. The testingmaintains the last maximum load for the test with the flaw to avoidoverload effect, but changes the minimum load. The same process astesting with flaw is used and may need to be repeated until thethreshold stress is achieved for the crack.

Referring now also to FIG. 24, the tests can be performed with variousstress ratios R for the coupons of same notch size a₀, which togethergenerate a threshold stress curves {s_(mean), s_(osc)} for notch lengtha_(0.1). In same way, the threshold stress curves can be achieved forvarious flaw sizes, shown as solid lines 2401, 2403, 2405 in FIG. 24.Similarly, the data obtained for various crack lengths can also form thethreshold stress curves for no-growth of crack(s), shown as dotted lines2402, 2404, 2406 in FIG. 24. Regarding FIG. 24, exemplary thresholdstress data generated via the test method is illustrated, wherein(a_(0,1)<a_(0,2)<a_(0,3)).

Referring now to FIG. 1 in the drawings, a rotorcraft 101 isillustrated. Rotorcraft 101 can have a rotor system 103 with a pluralityof rotor blades 105. The pitch of each rotor blade 105 can bemanipulated in order to selectively control direction, thrust, and liftof rotorcraft 101. Rotorcraft 101 can further include a fuselage 107,anti-torque system 109, and an empennage 111. The structure ofrotorcraft 101 can include a variety of airframe structures, such asbulkheads, ribs, longerons, stringers, keels, skins, spars, to name afew examples. A bulkhead 113 is labeled for illustrative purposes.

The methods and systems of the present disclosure relate to determiningdamage tolerance (“DT”) allowables for a structure, such as an aircraftstructure. It should be appreciated that rotorcraft 101 is merelyillustrated as one of many different types of aircraft whose structurecan be analyzed and designed using the methods and systems of thepresent disclosure. Furthermore, other aircraft can include, fixed wingaircraft, hybrid aircraft, unmanned aircraft, tiltrotor aircraft, toname a few examples.

Referring now also to FIG. 2, a method 201 of directly determiningdamage tolerance allowables is schematically illustrated. In oneembodiment, method 201 is a test method for determining no-growththreshold stress for a flaw or a crack in a metallic component.Applicable metals can include at least one of the following: aluminum,titanium, magnesium, steel, or an alloy thereof, to name a few examples.The conventional ASTM E647 method derives crack growth threshold (AKTH)from the derived crack growth rate curve (da/dN vs. AK) that is based oncrack growth testing a-N data, where K is stress intensity factor (SIF).Once AKTH is derived, it is further converted into no-growth thresholdfatigue stress. As a contrast, the direct test method 201 can generate afatigue stress data in which a flaw or a crack will not grow. In thisway, the no-growth damage tolerance allowables can be determined basedon the directly obtained fatigue test stress data.

Method 201 can include a step 203 of preparing a specimen, a step 205 ofcalculating an initial load, a step 207 of testing the specimen, and astep 209 of processing data. Each of these steps are described infurther detail herein.

Alternating or Oscillatory Stress (σ_(osc)): The alternating stress isone half of the stress range during a stress cycle.

Maximum Stress (σ_(max)): The highest algebraic value of stress in thestress cycle, tensile stress being considered positive and compressivestress negative.

Mean Stress (Steady Stress, σ_(mean)): The algebraic mean of the maximumand minimum stress in one stress cycle. A tensile stress is consideredpositive.

Minimum Stress (6 min): The lowest algebraic value of the stress in thestress cycle.

Scatter: This term usually refers to the scatter of test points whichdefine a σ_(osc)-σ_(mean) curve.

Stress Cycle (N): A stress cycle is the smallest section of thestress-time function which can be repeated periodically and identically.

Stress Ratio (R): The ratio of minimum stress divided by maximum stress.

Crack Initiation: In one example embodiment, crack initiation is when apre-crack appears beyond 0.001-inch but shorter than 0.004-inch(0.001-inch≤Δc_(i,o)≤0.004-inch), indicated by the potential drop method(PDM) during testing. i=1, 2, the two sides of gauge of the corner cracktest coupon on which notch (and crack) can be observed.

Initial Flaw Size (σ_(i,o)): Initial flaw size is defined as one of thedesign requirements for a DT part in which a flaw of the initial flawsize does not grow.

Initial Crack Size (σ_(i,c)): In one example embodiment, the initialcrack size is the size of crack initiation.

Crack Growth Increment (Δc_(i)): In one example embodiment, the crackgrowth increment is the length of crack initiation.

Initial Load (P_(o)): A load the test starts with.

Final Load (P_(C)): The load at which the notch starts to grow.

Test and Testing Block: A Test is an iterating process of stepped loadwith one time set up of testing frame. In one example embodiment, aTesting Block is counted as a 1,000,000 cycle run of fatigue test exceptthe last block for which the flaw/crack starts to grow before it reachesthe 1,000,000 cycles.

PD or PDM: Potential drop or potential drop method. A method to indicateoccurrence of crack growth by monitoring voltage change of a specialdetection system.

Referring now also to FIGS. 5-8, a specimen 501 which can also bereferred to herein as “Ks Bar”, is illustrated. In one exampleembodiment, specimen 501 is a bar coupon for an axially loaded fatiguetest that has a gauge of square cross-section and a corner notch 503 onthe middle plane of the specimen 501. As shown in FIG. 5, the specimen501 is symmetric about a center-plane.

Method 201 generates crack initiation data with using one or morespecimens 501, each with a corner notch 503 at the center-plane of thespecimen 501. In one implementation, three notch sizes can be utilized.Example nominal notch sizes for general metal-forming materials are0.005-inch, 0.010-inch, and 0.015-inch, measured on each side of thecorner of the specimen 501. Example nominal notch sizes for castingmaterials are 0.015-inch, 0.025-inch, and 0.050-inch, also measured oneach side of the specimen 501. For each notch size, twelve coupons canbe used to support the tests at five stress ratios, viz. R=−1, −0.5,0.05, 0.5, 0.8. Among these five stress ratios, R=0.05 is primary and atleast four specimens 501 can be used to support the R=0.05 tests. Forthe other four stress ratio tests, at least two specimens 501 can beused for each stress ratio tests. Table 1 lists an example specimenmatrix for the requirements of test specimens, i.e., thirty-six coupons.In addition, four un-notched spare specimens 501 can be used to mitigateunexpected events, resulting in a total of forty coupons that can beused in the example test program. It should be appreciated that theexact quantity of specimens 501 used in method 501 is implementationspecific; furthermore, the quantity of specimens 501 described hereinare for exemplary purposes and are not intended to be restrictive.

TABLE 1 Specimen Matrix Stress Ratio c_(i,o) (in) −1 −0.5 0.05 0.5 0.8Wrought Casting Specimen Number Total 0.005 0.015 TBD 0.010 0.025 TBD0.015 0.050 TBD Spare TBD TBD Total TBD

Depending on the probable flaw (or crack) orientation in a structuralpart for which the threshold stress data of the material is desired, thespecimen 501 is machined from the material direction so that the cornernotch 503 of the specimen 501 is of the same material orientation as inthe structural part.

For instance, a probable flaw in the S-T (or R-C) material orientationis possible in a structural part and no-growth threshold stress data isneeded. For wrought materials, the axial direction of the specimen 501can align with the thickness direction if it is made from a thick plate,or can align with the radius direction if it is made from a round bar.With this alignment, the corner notch 503 of a specimen 501 is in theS-T or R-C orientation. There may not be a specific requirement onalignment of the specimen 501 with respect to the sand casting materialsince the grain direction is not significant in such a case. The lengthof the specimen 501 can be any implementation specific length; however,one example length is approximately four inches. Another example lengthis five inches. The head buttons 505 a and 505 b of the specimen 501 aredesigned for the axial load application, for which the perpendicularityof the shoulders to the axis of the specimen 501 is desired during thetest.

In the example embodiment, a gauge section 507 is of squarecross-section. The center cross-section of the gauge section 507 is themid-plane (also symmetric plane) of the specimen 501, on which a notch503 is induced at a corner, as shown at least in FIGS. 7 and 8. Thenotch 503 includes a pair of lateral side walls 502 a and a root 502 bdisposed therebetween. In one example embodiment, the nominal dimensionsof corner notch 503 is c_(i,0)=0.05, 0.010, or 0.015 for metal-formingmaterials and 0.015, 0.025, or 0.050 for casting materials, where i=1(Side 1) and 2 (Side 2), measured from the corner point of the specimen501 to the tip of the notch 503 on each side of the gauge, as shown inFIG. 8. In one example embodiment, the width W of the corner notch 503is 0.003-inch. It is desired that the root 502 b of the corner notch 503(also called notch front) have a curved portion R1 as shown in FIGS. 7and 8.

The material of the specimen 501 should be the same as the material asthe structural part of which the damage tolerance allowables are beingdetermined. For example, the material of the specimen 501 should notonly be of the same material, but also have the same materialconditions, such as ultimate tensile strength (UTS), heat-treatment,hardening condition, and material form, as the structural part of whichthe damage tolerance allowables are being determined.

In one example embodiment, notch 503 is generated using an electricaldischarge machining (EDM) method; however, it should be appreciated thatother methods of creating notch 503 may be used, such as sawing,broaching, milling, machining with microtools, or laser cutting, forexample, as long as a notch can be created with a curved portion R1. Thestep of generating the notch 503 can include removing a portion of thematerial from the corner of the gauge section 507 of the specimen 501 toform the notch 503 having the lateral side walls 502 a and root 502 bdisposed therebetween. During the removing step as the material iscleared away (e.g., burned or cut away) from the corner to form thenotch 503 a portion of the remaining material in the root 502 b and/orside walls 502 a of the notch 503 is heated, softened, and thenhardened, which forms a re-melt material layer 504 thereon. The re-meltmaterial layer 504 has a high hardness due to being heated, softened,and then hardened during the generating a notch step. For example, butnot limitation, the re-melt material layer 504 can be caused by the hightemperatures that occur during the EDM method.

Referring to FIGS. 19-22 and 25A-25B, a portion of notch 503 ismetallurgically depicted. A post-notching selective surface treatmentmethod can be desirable to modify the EDM corner notch of the specimen501 for flaw simulation. One purpose of the treatment method is toremove at least a portion of the re-melt material layer 504 from asurface of the notch 503. In an exemplary embodiment, the notchtreatment method includes removing at least a portion of the re-meltlayer 504 from the root 502 b of the notch 503. In other embodiments,the notch treatment method includes removing at least a portion of there-melt layer 504 from the lateral sides 502 a of the notch 503. Anotherimportant purpose of the treatment method is to chemically attack andweaken the grain boundaries 512 on the etched surface 510 of notch 503to make the evaluation more conservative. FIG. 19 shows an example of acorner notch 503 produced with an EMD process. FIG. 20 is a close-upview of the root 502 b of the notch 503 with a re-melt layer 504 beforea treatment method. FIG. 21 is a close-up view of root 502 b of thenotch 503 after a treatment method showing an etched surface 510 in theroot 502 b of the notch 503. FIGS. 25A-25B is another close-up view ofroot 502 b of the notch 503 before and after a treatment method. FIG.25A shows an un-etched notch surface 509 including a re-melt layer 504on the root 502 b; FIG. 25B shows an etched surface 510 on the root 502b. A comparison between FIGS. 20, 25A and FIGS. 21, 25B, respectively,reveals that the re-melt material layer 504 has been removed (e.g.,disintegrated) from the etched surface 510 on notch 503 after a notchtreatment method 551. This results in a desired notch severity (worstnotch) for the test. The notch 503 with the etched surface 510 in theroot 502 b can be representative of the worst-case defects (e.g., themost unfavorable manufacturing flaws and operational defects) of thesame size. For example, the notch 503 with the etched surface 510 can berepresentative of other types of defects of the same size such as, butnot limited to, a dent, a scratch, a ding, corrosion, an inclusion, asurface flaw, a corner flaw, an inner flaw, a corrosion pit, a burr, ashotpeened overlap, a void, a pore, a fold, nonhomogeneity, and aforging parting plane.

Referring now to FIG. 26A, an exemplary embodiment of a notch treatmentmethod 551 for flaw simulation is schematically illustrated. Method 551can include a step 553 of providing the specimen with a notch 503, thenotch 503 having a re-melt material layer 504 in a root of the notch; astep 555 of isolating the notch 503; a step 557 of selectively etchingthe notch 503 with an etching solution to provide an etched surface 510at the root 502 b of the notch 503; and a step 559 of cleaning thespecimen. Each of these steps are described in further detail herein.

Method 551 includes the step 553 of providing the specimen with thenotch 503, the notch having a re-melt material layer 504. Method 551 canbe utilized for a specimen comprised of an applicable metal such as, butnot limited to, aluminum, titanium, magnesium, steel, or an alloytherefor. Step 553 can include generating a notch 503 using EDM. In anillustrative embodiment, the notch 503 created by EDM can cause are-melt material layer 504 comprised of the specimen alloy mixed withtungsten (e.g., from the tungsten wire used by the EDM) in the notch503. The re-melt material layer 504 can be approximately 0.0001 inchesthick and tends to be brittle in nature and differs in crystallinestructure from the material to be tested. The brittle nature of there-melt material layer 504 causes the root 502 b of the notch 503 to besusceptible to premature cracking from test loading, to change thecracking mode, and to modify the desired testing outcome (e.g., thetesting results may be inaccurate, too conservative, non-conservative,or variable).

Method 551 includes the step 555 of isolating the notch 503. In anembodiment, the step 555 can include cleaning of the specimen 501 toremove any unwanted debris and/or oils; for example, but not limitation,the specimen 501 can be submersed in liquid acetone for ultrasoniccleaning and acetate tape can be applied to the notch 503 to removedebris therein.

The step 555 of isolating the notch 503 can include placing an isolationlayer 519 with a slot 521 on to the specimen 501 such that the slot 521exposes the notch 503 as shown in FIGS. 27 and 28. The isolation layer519 can be an opaque polytetrafluoroethylene (PTFE) adhesive tapecommercially available from 3M Company. Step 555 can include cutting aslot 521 in the isolation layer 519 having the dimensions of the notch503. The isolation layer 519 with the slot 521 is then placed on thespecimen 501 such that the slot 521 aligns with and exposes the notch503. Any air bubbles between the isolation layer 519 and the specimen501 are removed by pressing down on the isolation layer 519. In anillustrative embodiment shown in FIG. 28, the isolation layer 519 withthe slot 521 is disposed in the gauge section 507 of the specimen 501.

The step 555 of isolating the notch 503 can include placing a dam 523 onthe isolation layer 519 to form a notch area N1 and a peripheral area P1on the specimen 201 as shown in FIGS. 29 and 30. The notch area N1 is onthe inside of the dam 523 and the peripheral area P1 is on the outsideof the dam 523. The notch area N1 is disposed at least partially aroundthe notch. In some preferred embodiments, the notch 503 is substantiallyin the center of the notch area N1.

In an illustrative embodiment, the step of placing a dam 523 on theisolation layer 519 can include forming a moldable cylinder. The dam 523can be formed from a moldable material such as a sealant tapecommercially available as Tacky Tape commercially available fromIllinois Tool Works Inc. The moldable material can be formed by curlingor molding to form a complete cylinder, as shown in FIGS. 29 and 30. Thedam 523 is then placed on the isolation layer 519 on the specimen 501such that all bottom edges are touching the isolation layer 519. Thespecimen 501 with the isolation layer 519 and the dam 523 is placed in arotatable vise and positioned so the dam 523 is oriented vertically andopen at the top, as shown in FIG. 30.

Method 551 includes the step 557 of selectively etching the notch 503 toprovide an etched surface 510 of the notch 503. The step 557 can includeapplying an etching solution to the notch area N1 to form the etchedsurface 510 of the notch 503. The etching solution can include at leastone of the following: a sodium hydroxide solution, a Kroll's etchantsolution, an acetic acid solution, an aqua regia solution, a Fry'sreagent solution, and a nital solution. Each of these etching solutionsare described in further detail herein. It should be noted that the step557 of selectively etching is described using chemicaletching/modification. In some embodiments, the step 557 of selectivelyetching can include electro-etching, blast erosion, or other etchingprocedures separate from or along with chemical etching/modification.

Method 551 includes the step 559 of cleaning the specimen 501. The step559 of cleaning the specimen can include the steps of removing theisolation layer 519 and the dam 523 from the specimen 501 and cleaningthe specimen to remove the etching solution and any debris or othercontaminates. The step 559 of cleaning the specimen 501 is described infurther detail herein.

In a particular embodiment, the specimen 501 comprises aluminum or analloy thereof and the etching solution is a sodium hydroxide solution.In an exemplary embodiment, the sodium hydroxide solution is 10 g ofNaOH mixed in 90 ml of de-ionized water. To etch the notch 503, the dam523 is filled with the sodium hydroxide solution from about 6 minutes toabout 15 minutes as required for the size and depth of the notch 503,with occasional agitation. After selectively etching the notch 503 toform an etched surface thereon, the aluminum specimen is then cleaned byremoving the sodium hydroxide solution, dam 523, and isolation layer519. The aluminum specimen 501 can then be flushed with isopropylalcohol and hot air dried. The notch 503 can undergo further cleaning bywiping a nitric acid solution (50% in water) with a cotton swab thereonand then flushed with water and then isopropyl alcohol and dried.

In a particular embodiment, the specimen 501 comprises titanium or analloy thereof and the etching solution is a Kroll's etchant solution. Inan exemplary embodiment, the Kroll's etchant solution is 8 ml of HF, 30ml of HNO₃ and 62 ml of H₂O. To etch the notch 503, the dam 523 isfilled with the Kroll's etchant solution from about 4 minutes to about12 minutes as required for the size and depth of the notch 503. Afterselectively etching the notch 503 to form an etched surface thereon, thetitanium specimen is then cleaned by removing the Kroll's etchantsolution, dam 523, and tape 519. The titanium specimen 501 can then beflushed with water and then with isopropyl alcohol and hot air dried.

In a particular embodiment, the specimen 501 comprises magnesium or analloy thereof and the etching solution is an acetic acid solution. In anexemplary embodiment, the acetic acid solution is 1 ml of HNO₃, 25 ml ofH₂O, 14 ml of acetic acid, and 60 ml of ethylene glycol or diethyleneglycol. To etch the notch 503, the dam 523 is filled with the aceticacid solution from about 5 minutes to about 12 minutes as required forthe size and depth of the notch 503. After selectively etching the notch503 to form an etched surface thereon, the magnesium specimen is thencleaned by removing the acetic acid solution, dam 523, and tape 519. Themagnesium specimen 501 can then be flushed with water and then withisopropyl alcohol and hot air dried.

The step 559 of cleaning the specimen 501 can include preserving thespecimen 501 to prevent debris and corrosion of the specimen 501 andnotch 503. The etched surface 510 of the notch 503 is viewed anddocumented by photomicrographs at the necessary magnification.

Referring now to FIG. 26B, another exemplary embodiment of a treatmentmethod 571 for flaw simulation is schematically illustrated. Method 571can include a step 573 of providing the specimen with a notch 503, thenotch 503 having a re-melt material layer 504; a step 575 of isolatingthe notch 503; a step 577 of selectively etching the notch 503 with afirst etching solution and a second etching solution to provide anetched surface 510 of the notch 503; a step 579 of cleaning thespecimen; and a step 580 of applying a heat treatment to the specimen.The steps 573 and 575 in method 571 are substantially similar to thesteps 553 and 555 in the method 551; therefore, for sake of efficiencyonly the steps 577, 579, and 580 will be described in further detailherein. However, one of ordinary skill in the art would fully appreciatean understanding of the steps 573 and 575 based upon the disclosureherein of the steps 553 and 555 in the method 551.

The step 577 can include applying a first etching solution and a secondetching solution to the notch area N1 to form an etched surface 510 ofthe notch 503. In a particular embodiment, the specimen 501 comprisessteel and the first etching solution is an aqua regia solution comprisedof HCl/HNO₃ (3:1 ratio). In an exemplary embodiment of selectivelyetching the notch 503, the dam 523 is filled with the aqua regiasolution from about 30 seconds to 4 minutes as required for the size anddepth of the notch 503 and type of steel. The aqua regia solution isthen discarded from the dam 523 and the second etching solution isfilled in the dam 523.

In an embodiment, the specimen 501 is a stainless steel and the secondetching solution is a Fry's reagent solution designated as ASTM standardE 407 formula number 79 “Fry's”. The dam 523 is filled with the Fry'sreagent solution from about 2 minutes to about 5 minutes as required forthe size and depth of the notch 503. The step of 579 of cleaning thestainless steel specimen 501 can include discarding the Fry's reagentsolution from the dam 523, removing the tape 519 and dam 523, flushingthe specimen 501 with water and then isopropyl alcohol, and drying usinghot air.

In an embodiment, the specimen 501 is a high strength steel and thesecond etching solution is a nital solution. In an embodiment, the highstrength steel is a nickel-chromium-molybdenum alloy steel. The nitalsolution can comprise a 5% nitric acid (by volume) and alcohol (e.g.,methanol, ethanol, or methylated spirits) solution. The dam 523 isfilled with the nital solution from about 8 minutes to about 15 minutesas required for the size and depth of the notch 503. The step of 579 ofcleaning the high strength steel specimen 501 can include discarding thenital solution from the dam 523, removing the tape 519 and dam 523,flushing the specimen 501 with water and isopropyl alcohol, and dryingusing hot air.

In an embodiment, the step 580 of applying a heat treatment to thespecimen 501 occurs within 1 hour of step 579. The step 580 of applyingheat is selectively adjusted for the type of steel and the requiredtensile strength for the aircraft component. In an exemplary embodiment,the heating temperature can be from about 250 degrees Fahrenheit toabout 400 degrees Fahrenheit for about 3 hours to about 30 hours.

The step 579 of cleaning the specimen 501 can include preserving thespecimen 501 to prevent debris and corrosion of the specimen 501 andnotch 503. The etched surface 510 of the notch 503 is viewed anddocumented by photomicrographs at the necessary magnification.

In some embodiments, the notch treatment methods 551, 571 can penetrate,disintegrate, and dissolve at least a portion of the re-melt materiallayer from the notch 503. The treatment methods 551, 571 canadvantageously remove at least a portion of the re-melt material layerfrom the notch 503. Moreover, the treatment methods 551, 571 can provideat least a portion of the etched surface 510 with microcracks extendingfrom weakened grain boundaries 512, as shown in FIG. 31, which is a viewof an etched surface 510 at a magnification of 300X. In someembodiments, the microcracks can include micro-pits in the etchedsurface 510, as shown in FIG. 25B. Microcracks form at the grainboundaries 512 of the etched surface 510 as a result of the treatmentmethods 551, 571. The treatment methods 551, 571 weaken the grainboundaries 512 on the etched surface 510 of the notch 503 (e.g., thenotch surface after undergoing a treatment method 551, 571). Thetreatment methods 551, 571 advantageously provide an etched surface 510on notch 503, which is representative of several worst-case defects ofthe same size. The treatment methods 551, 571 for flaw simulation canadvantageously simplify the overall testing and analysis of specimensused to determine damage tolerance allowables for an aircraft structure.

FIG. 22 illustrates the notch 503 in a specimen 501 that has beensectioned at the crack plane after testing. Such a sectioning ofspecimens 501 can be performed to verify notch measurements and crackmeasurements using a scanning electron microscope (SEM) measurement, forexample. Etching of the notch 503 results in an etched notch surface 510on sides 502 a and in the root 502 b. During testing, a first stagecrack growth 517 is created, which exists between notch root 502 b and afirst detected crack front 511. As discussed further herein, the test istemporarily halted upon detection of the first crack 511. The test canbe resumed until a second stage crack growth 506 is created betweenfirst detected crack front 511 and a second detected crack front 513.

Now referring to FIG. 9, an exemplary specimen ID 901 can be utilized tomark each specimen 901 to keep track of critical information and insureaccurate test data. The specimen ID 901 can include information such as:Test Request (TR) number, the location that specimen blank is cut outfrom the stock material, the notch size, and the stress ratio at whichthe coupon will be tested, as illustrated in FIG. 9.

Referring again to FIG. 2, method 201 further includes a step 205 ofcalculating an initial load. The step 207 of testing the specimen(s) 501is an iterative process that starts with an initial load to converge theload to the point at which the flaw starts to grow. A reference da/dNvs. AK curve is preferred to narrow the range for the initial loaddetermination. The reference information can be an existing AKTH data ora plot of da/dN vs. AK curves referred for the material to be tested orfor the materials that have characteristics similar to that to betested. These characteristics include the chemical elements of thematerial, ultimate tensile strength (UTS), material form, and materialtreatments. FIG. 10 is an example of a da/dN vs. AK curve 1001 forTi-6Al-4V.

Step 205 can further include using a stress intensity factor (SIF) tocalculate the initial load. SIF equations for a corner notch (crack) ofa square bar can be used in the initial load calculation. In one exampleembodiment, a correction factor can be used to account for geometricaleffects on SIF. FIG. 8 depicts geometries and loading application forthe test procedure. Table 2 lists the notations of FIG. 8 and theassociated descriptions.

TABLE 2 Specimen Matrix Symbol Description b₁ Width of the cross-sectionon the side of the gauge aligning with L-direction b₂ Width of the crosssection on the side of the gauge align with T-direction S₀ Magnitude ofuniform remote stress c₁ Crack length measured on the side aligning withL-direction of the gauge c₂ Crack length measured on the side aligningwith T direction of the gauge

Method 201 is an iterative process which can include an interval ofcycles, such as 1,000,000 cycles for example, for each step of iterationuntil a flaw (or a crack) starts to grow. In order to determine the loadat which a flaw starts to grow, the test starts with an initial load anditerates with the calculated load increments until the flaw grows. Theinitial load can be determined based on the reference threshold AKTH forstress ratio R₀=0 and the traditional A=0.8 approximation fordifferentiated stress ratio R₁. Starting with the reference AKTH,Equations 1-8 are the basis to determine initial load from stressintensity factor (SIF) for a corner crack initiation test. Byre-arranging Equation 1, with the support of Equations 2-8 and Table 3,the remote stress S₀ can be calculated. Multiplying S₀ by area of gaugecross-section, the initial load can be determined.

$\begin{matrix}{K = {F_{0}S_{0}\sqrt{\pi\; c}}} & (1) \\{F_{0} = {f_{x}f_{\varnothing}f_{a}f_{0}}} & (2) \\{{f_{x} = \left\lbrack {1 + {1.464\left( \frac{c\; 1}{c\; 2} \right)^{1.65}}} \right\rbrack^{- \frac{1}{2}}},\mspace{14mu}{{{for}\mspace{14mu}\frac{c\; 1}{c\; 2}} \leq 1}} & (3) \\{{f_{x} = \left\lbrack {1 + {1.464\left( \frac{c\; 2}{c\; 1} \right)^{1.65}}} \right\rbrack^{- \frac{1}{2}}},\mspace{14mu}{{{for}\mspace{14mu}\frac{c\; 1}{c\; 2}} > 1}} & (4) \\{{f_{\varnothing} = \left\lbrack {\left( {\frac{c\; 1}{c\; 2}\cos\;\varnothing} \right)^{2} + {\sin^{2}\varnothing}} \right\rbrack^{\frac{1}{4}}},\mspace{14mu}{{{for}\mspace{14mu}\frac{c\; 1}{c\; 2}} \leq 1}} & (5) \\{{f_{\varnothing} = \left\lbrack {{\cos^{2}\varnothing} + \left( {\frac{c\; 2}{c\; 1}\sin\;\varnothing} \right)^{2}} \right\rbrack^{\frac{1}{4}}},\mspace{14mu}{{{for}\mspace{14mu}\frac{c\; 1}{c\; 2}} > 1}} & (6) \\{{\phi = {0{^\circ}\mspace{14mu}{at}\mspace{14mu} c_{2}\text{-}{tip}}},{\phi = {90{^\circ}\mspace{14mu}{at}\mspace{14mu} c_{1}\text{-}{tip}}}} & \; \\{{f_{a} = 1},\mspace{14mu}{{{for}\mspace{14mu}\frac{c\; 1}{c\; 2}} \leq 1}} & (7) \\{{f_{a} = \sqrt{\frac{c\; 2}{c\; 1}}},\mspace{14mu}{{{for}\mspace{14mu}\frac{c\; 1}{c\; 2}} > 1}} & (8) \\{f_{0} = {{Tabular}\mspace{14mu}{data}\mspace{14mu}\left( {{Table}\mspace{14mu} 301\mspace{14mu}{in}\mspace{14mu}{{FIG}.\mspace{14mu} 3}} \right)}} & \;\end{matrix}$

Referring again to FIG. 2, method 201 further includes a step 207 oftesting the specimen(s) 501. Step 207 includes iteratively loading aspecimen 501 at stepped loads for an implementation specific number ofcycles until a flaw (or a crack) starts to grow in corner notch 503. Thetest process in step 207 starts with an Initial Load (P₀) and ends atthe Final Load (P_(C)) at which the flaw (or crack) starts to grow. Eachtest determines the Final Load, Mean Stress, and Oscillatory Stress forthe given flaw size, stress ratio, and limited cycles.

Referring also to FIG. 11, pretest data can include: 1) gauge sectiondimensions t and W (measurements), 2) notch dimensions a₀, c₀, and b,where b is the width of the notch (measurements), 3) stress ratio R, 4)Initial Load P₁, 5) final crack length a_(c) and c_(c), 6) testingfrequency, and 7) lab temperature (recorded by the testing lab), and 8)lab humidity (recorded by the testing lab).

After entering any pretest data, the testing step 207 can furtherinclude: installing the specimen 501, tuning for alignment, calibratingthe measurement and data acquisition system, setting P_(max) and P_(min)for cyclic load, setting potential drop (PD) using a needle-springmethod.

Referring also to FIG. 12, a specimen 501 is illustrated installed in atest setup. A first needle 1203 and a second needled 1205 are pressedagainst either side of the notch 503. During testing, a current ispassed through the notch 503 between needles 1203 and 1205. Thedetection of crack growth is a result of a change in electricalresistance between needles 1203 and 1205. The utilization of needles1203 and 1205 in a PD system 1201 prevents the need for welding orotherwise attaching sensors that could prove an undesired cracking orannealing of the specimen 501. In one example embodiment, the PD system2101 is set such that the test stops when Δa=(0.001˜0.004) inch, forexample. In one example embodiment, the cycle count (N) is set to zeroprior to the start of a test block, and the maximum cycle number is setto 1,000,000 for a testing block such that the test stops at N=1,000,000if no Δa is detected.

Referring again to FIG. 11, step 207 of method 201 is illustrated in ablock diagram format. Step 207 can be broken down between a constant Rtesting loop 1101 and a constant P_(max) testing loop 1103. Each of theconstant R testing loop 1101 and a constant P_(max) testing loop 1103are discussed further herein.

The constant R testing loop 1101 can include starting the test with thePD 1201 turned on and cycle count on. If a crack extension is detectedvia the PD 1201, the test is stopped, as shown in graph 1301 of FIG. 13.In the illustrated graph 1301, a crack extension is detected atoccurrence 1303, which is as a point in time short of the first full1,000,000 cycles. Next the crack dimensions are measured. In one exampleembodiment, the dimensions of the crack, such as first crack 517, can bemeasured by an optical microscope on the sides of specimen 501 while thespecimen is still attached to the test setup. If crack dimensions exceedthe given final crack length a_(c) and c_(c), the test is completed andthe results are reported. If crack dimensions do not reach a_(c) andc_(c), then the test proceeds to the next step. If a crack extension isnot detected, the test continues until 1,000,000 cycles are reached anda testing block is considered completed. An example completed testingblock that did not experience crack extension is illustrated as testingblock 1405 as shown by graph 1401 in FIG. 14. The next step-load isprepared, the cycle count is reset to zero, and the test restarted. Thesteps are repeated until a crack extension is detected or until“stop-test”, whichever comes first, then the constant R testing loop1101 (FIG. 11) is exited. In the illustrated graph 1401, a crackextension is detected at occurrence 1403, which is as a point in timeafter two full 1,000,000 cycles, but short completion of the thirdstepped 1,000,000 cycle testing block.

The constant P_(max) testing loop 1103 with stepped P_(min), constantP_(max), and varying R can include resetting cycle count to zero andresetting loads with an increased P_(min) while keeping the P_(max) thesame as that at the constant R loop 1101. Next the test is resumed withcycle count and PD 1201 turned on. If a crack extension is detected atan occurrence 1503 via PD, the test is stopped, as shown in graph 1501of FIG. 15. Next the extended crack dimension is measured. If the crackdimension exceeds the given final crack length a_(c) and c_(c), the testis completed. If the crack dimensions do not reach a_(c) and c_(c), thenthe test continues to the next step. If a crack extension is notdetected by PD 1201, the test continues until 1,000,000 cycles arereached at occurrence 1603 and a testing block is considered completed,as shown in graph 1601 of FIG. 16. The results are reported and theprocess proceeds with the next step-load and instructions. The steps arerepeated until a crack extension is detected at an occurrence 1605 oruntil “stop-test”, whichever comes first, then the constant P_(max)testing loop 1103 (FIG. 11) is exited.

Method 201 can also include a step 209 of processing the data from thetest. Step 209 is intended to extract the specimen and testinginformation for each test and determine the validity of the testingresult data. Valid data for a threshold testing program can be definedas the data at the crack initiation (or extension) Δa/ΔN≤4×10⁻⁹in/cycle. If this criterion is met at the crack initiation, the load isvalid as a threshold for no-growth. If the threshold criterion is notmet at the crack initiation, the previous run-out load can be usedinstead.

The immediate test data are the no-growth threshold fatigue loads, i.e.maximum load P_(max) and minimum load P_(min), from which fatigue meanand oscillatory load P_(mean) and P_(osc) can be converted:P _(mean)=(P _(max) +P _(min))/2  (Eq. 1)P _(osc)=(P _(max) −P _(min))/2  (Eq. 2)

The no-growth threshold stresses can be calculated as loads divided bynotch plane area A:S _(mean) =P _(mean) /A  (Eq. 3)S _(osc) =P _(osc) /A  (Eq. 4)

Data can be organized in categories of flaw and crack. Under eachcategory, data can be grouped by nominal notch dimensions. In caseswhere the actual notch/crack length is not the same as nominal length,an adjustment can be made based on geometrical parameter β of LinearElastic Fracture Mechanics (LEFM):S _(nominal) =S _(actual)(β_(actual)/β_(nominal))√(a _(0,actual) /a_(0,nominal))  (Eq. 5)

For example, in a group of a₀=0.010-in, the actual notch dimensions canbe measured as 0.012, 0.009, 0.010, 0.012, 0.010, 0.008, 0.011, etc. TheLEFM adjustment can be made to collapse the non 0.010-in data onto0.010-in equivalent. Similarly, the data can be adjusted if the cracklengths that are measured during testing are different from the actualcrack lengths determined in a post-test measurement.

Table 3 shows an example of organized geometrical and testing resultsdata of a material for a nominal a₀=0.010-in group. Based on this datatable, the threshold loads are determined and the threshold stresses arecalculated accordingly.

TABLE 3 Example Data Table of Organized Geometrical and Test ResultsData Run- out P_(max) at Notch Specimen 0′ - Notch 1 - Crack (at P_(max)last Length # c_(1,0) c_(2,0) c_(1,c) C_(2,c) b1 b2 R N break)(previous) run? c₁/c₂ ΔC,min ΔC,max 0.010 TR4473- 0.0115 0.0105 0.01600.0150 0.2593 0.2607 −1 643,483 1,808 1,469 no 1.095 0.0045 0.005 B1-103-1 TR4473- 0.0100 0.0098 0.0110 0.0110 0.2597 0.2592 −1 33,370 1,9001,543 no 1.020 0.001 0.001 B2- 103-1 TR4473- 0.0118 0.0107 0.0210 0.01500.2600 0.2600 0.05 59,278 3,087 2,487 no 1.103 0.004 0.009 B5- 103-3TR4473- 0.0092 0.0110 0.0130 0.0130 0.2597 0.2606 0.05 182,745 3,2052,787 no 0.836 0.002 0.004 B6- 103-3 TR4473- 0.0127 0.0106 0.0127 0.01060.2594 0.2603 0.05 1,000,000 2,752 2,061 yes 1.198 0.000 0.000 B8- 103-3TR4473- 0.0098 0.0093 0.0098 0.0093 0.2603 0.2604 0.50 1,000,000 4,6113,747 yes 1.054 0.000 0.000 B9- 103-4 TR4473- 0.0093 0.0106 0.00930.0106 0.2606 0.2606 0.74 1,000,000 6,621 0 yes 0.877 0.000 0.000 B11-103-5 TR4473- 0.0093 0.0106 0.0093 0.0106 0.2606 0.2606 0.80 1,000,0006,621 5,857 yes 0.877 0.000 0.000 B11- 103-6

After data for all groups and categories are analyzed, they can beplotted in a graph 1701 as shown in FIG. 17 as threshold stresses forno-growing flaw and crack for the material. For each flaw/crack length,a curve fit is generated based on the lowest data points.

Referring now to FIG. 4, a method 401 of a designing and manufacturing apart or structure of an aircraft, such as rotorcraft 101, isschematically illustrated. An illustrative structure is bulkhead 113,shown in FIG. 1. A step 403 can include designing a structure with acomputer aided design (CAD) tool which can include defining apreliminary geometry of the structure. Step 403 can include performing astress analysis of the structure, this analysis can include analyticallysubjecting the structure to loads, calculating the stress, andevaluating the stress with regard to the damage tolerance allowables,the damage tolerance allowables being calculated using method 201described herein. Step 403 can include iteratively changing the geometryof the part until a weight efficient configuration is reached. In oneembodiment, the geometry of the structure is iteratively optimized so asto meet the stress allowables without having unnecessary weight. A step405 can include manufacturing the structure to the geometry defined instep 403.

Referring now also to FIG. 18, a computer system 1801 is schematicallyillustrated. Computer system 1801 can be configured for performing oneor more functions with regard to the operation of system and methodfurther disclosed herein. Further, any processing and analysis can bepartly or fully performed by computer system 1801. Computer system 1801can be partly or fully integrated with other aircraft computer systems.

The system 1801 can include an input/output (I/O) interface 1803, ananalysis engine 1805, and a database 1807. Alternative embodiments cancombine or distribute the input/output (I/O) interface 1803, analysisengine 1805, and database 1807, as desired. Embodiments of the system1801 can include one or more computers that include one or moreprocessors and memories configured for performing tasks describedherein. This can include, for example, a computer having a centralprocessing unit (CPU) and non-volatile memory that stores softwareinstructions for instructing the CPU to perform at least some of thetasks described herein. This can also include, for example, two or morecomputers that are in communication via a computer network, where one ormore of the computers include a CPU and non-volatile memory, and one ormore of the computer's non-volatile memory stores software instructionsfor instructing any of the CPU(s) to perform any of the tasks describedherein. Thus, while the exemplary embodiment is described in terms of adiscrete machine, it should be appreciated that this description isnon-limiting, and that the present description applies equally tonumerous other arrangements involving one or more machines performingtasks distributed in any way among the one or more machines. It shouldalso be appreciated that such machines need not be dedicated toperforming tasks described herein, but instead can be multi-purposemachines, for example computer workstations, that are suitable for alsoperforming other tasks.

The I/O interface 1803 can provide a communication link between externalusers, systems, and data sources and components of the system 1801. TheI/O interface 1803 can be configured for allowing one or more users toinput information to the system 1801 via any known input device.Examples can include a keyboard, mouse, touch screen, and/or any otherdesired input device. The I/O interface 1803 can be configured forallowing one or more users to receive information output from the system1801 via any known output device. Examples can include a displaymonitor, a printer, cockpit display, and/or any other desired outputdevice. The I/O interface 1803 can be configured for allowing othersystems to communicate with the system 1801. For example, the I/Ointerface 1803 can allow one or more remote computer(s) to accessinformation, input information, and/or remotely instruct the system 1801to perform one or more of the tasks described herein. The I/O interface1803 can be configured for allowing communication with one or moreremote data sources. For example, the I/O interface 1803 can allow oneor more remote data source(s) to access information, input information,and/or remotely instruct the system 1801 to perform one or more of thetasks described herein.

The database 1807 provides persistent data storage for system 1801.While the term “database” is primarily used, a memory or other suitabledata storage arrangement may provide the functionality of the database1807. In alternative embodiments, the database 1807 can be integral toor separate from the system 1801 and can operate on one or morecomputers. The database 1807 preferably provides non-volatile datastorage for any information suitable to support the operation of thesystem and method disclosed herein, including various types of datadiscussed further herein. The analysis engine 1805 can include variouscombinations of one or more processors, memories, and softwarecomponents.

The particular embodiments disclosed herein are illustrative only, asthe system and method may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Modifications, additions, or omissionsmay be made to the system described herein without departing from thescope of the invention. The components of the system may be integratedor separated. Moreover, the operations of the system may be performed bymore, fewer, or other components.

Furthermore, no limitations are intended to the details of constructionor design herein shown, other than as described in the claims below. Itis therefore evident that the particular embodiments disclosed above maybe altered or modified and all such variations are considered within thescope and spirit of the disclosure.

To aid the Patent Office, and any readers of any patent issued on thisapplication in interpreting the claims appended hereto, applicants wishto note that they do not intend any of the appended claims to invokeparagraph 6 of 35 U.S.C. § 112 as it exists on the date of filing hereofunless the words “means for” or “step for” are explicitly used in theparticular claim.

The invention claimed is:
 1. A notch treatment method for flawsimulation, comprising: providing a specimen with a notch, the notchhaving a re-melt material layer, the specimen comprises titanium or analloy thereof; isolating the notch comprises placing an isolation layerwith a slot onto the specimen such that the slot exposes the notch andplacing a dam on the isolation layer to form a notch area and aperipheral area on the specimen, wherein the step of placing the dam onthe isolation layer comprises forming a moldable cylinder; andselectively etching the notch by filling the dam with an etchingsolution comprising Kroll's etchant solution to provide an etchedsurface of the notch; wherein at least a portion of the re-melt materiallayer has been removed from the notch; and wherein at least a portion ofthe etched surface on the notch includes microcracks.
 2. The treatmentmethod according to claim 1, wherein the step of providing the specimenwith the notch comprises: generating the notch on the specimen byelectrical discharge machining.
 3. The treatment method according toclaim 1, wherein the re-melt material layer is disposed on at least oneof a root notch and a lateral side wall of the notch.